An improved system of variability classification is used in the fourth
edition of the GCVS, based on recent developments in classification
principles and taking into account the suggestions of a number of
specialists. Variability types are grouped according to the major
astrophysical reasons for variability.

All of these classes include objects of a dissimilar nature that belong
to different types of light variability. On the other hand, an object
may be variable because of almost all of the possible reasons or because
of any combination of them. If a variable belongs to several types of
variability, the types are joined in the data field by a "+" sign, e.g.,
E+UG, UV+BY.

Despite considerable success in understanding stellar variability pro-
cesses, the classification adopted in the Catalogue is far from perfect.
This is especially the case for explosive, symbiotic and novalike
variables, X-ray sources, and peculiar objects.

The new variability types (ZZO, AM, R, BE, LBV, BLBOO, EP, SRS, LPB)
have been added in the Name-Lists 67- 77 and in the GCVS vol.V.

If a variable star belongs to several types of light variability
simultaneously, the types are joined in the type field by a "+" sign
(e.g., E+UG, UV+BY).